Resolution of chiral nitrogen atoms in 1D helical coordination polymers

A unique stereochemically labile secondary amine with a chiral nitrogen atom assemble cobalt and zinc ions in the aid of chelating ancillary ligands to give rise to three helical 1D coordination polymers, [Co(p-cpdba)(2,2'-bpy)](n) (1), {[Zn(p-cpdba)(2,2'-bPY)]}(n) (2) and [Zn(p-cpdba)(1,10-phen)](n) (3) (cpdba(2-) = 4-(4-carboxyphenylamino)-3,5-dinitrobenzolate, 2,2'-bpy = 2,2'-bipyridine, 1,10-phen = 1,10-phenanthroline). Compound 1 exhibits a racemic double-stranded chained structure with chelating 1,10-phen occupying two sites of the octahedral cobalt(11). By changing to five-coordinated square pyramidal zinc(II) and employing 2,2'-bpy and 1,10-phen, two triple-stranded chained compounds 2 and 3 are synthesized. As expected, all chiral nitrogen atoms within each chiral chain of every triple-stranded helix in 2 and 3 have the same absolute configuration due to the confining growth along one dimension. Therefore, the resolution of chiral nitrogen atom is achieved though only at a one-dimensional scale.